Moldable silicone elastomers having selective primerless adhesion

ABSTRACT

Organopolysiloxane compositions that cure by the addition reaction of silicon-bonded lower alkenyl radicals with silicon-bonded hydrogen atoms and which exhibit select adhesion to a variety of substrates. The compositions comprise an adhesion promoting mixture comprising an epoxy-functional compound, soluble polydiorganosiloxanes, polycycloorganosiloxanes (linear and cyclic) and and hydroxy end blocked hydrocarbons (glycols) thus giving release characteristics to metal substrates while maintaining adhesion to a thermoplastic substrate. Additionally, an additive may be used to produce surface lubricity after curing.

RELATED APPLICATION

This is a continuation in part of U.S. application Ser. No. 09/715,963filed Nov. 17, 2000 now U.S. Pat. No. 6,663,967.

FIELD OF THE INVENTION

The present invention relates both to a method for improving theprimeness adhesion of cured silicone elastomers and to curable (andcured) high strength, organopolysiloxane molding compositions useful toproduce cured silicone rubber articles that exhibit excellent adhesionto thermoplastic resins such as, but not limited to, PBT and PPA, whilenot significantly adhering to metal substrates.

BACKGROUND OF THE INVENTION

Moldable primerless organopolysiloxane compositions are known and used.One problem with all such compositions is that due to the adhesionadditives in the compositions they also adhere to metal surfaces. Inmolding processes, the typical mold is metal. It is difficult toselectively adhere to thermoplastic substrates without deleteriouseffects. Additionally, the kinetics and thermochemistry of the moldingprocess and the compositions used in such processes are such that onlysmall lightweight composite plastic and silicone elastomer articles ofmanufacture can be made by molding techniques because of the difficultyof removing the article from the metal mold.

Organopolysiloxane compositions useful for molding typically containalkenyl polymers, fillers, and other additives. The compositions containa platinum catalyst, a hydride crosslinker and cure inhibitors. Thesecan be one or two component systems that are mixed prior to the moldingprocess. These heat cured (i.e. high consistency or millable rubber) orliquid injection molded silicone rubbers are commonly available withoutadditives that improve adhesion.

Typical molding compositions generally include the followingingredients:

1) 100 parts by weight of a vinyl stopped polydimethylsiloxane having aviscosity ranging from 10,000 to 1,000,000 centipoises at 25° C. and avinyl content ranging from about 0.01 to 0.25 mole per cent;

2) up to 10 parts by weight of a low molecular weight vinyl stoppedvinyl on chain hydroxyl end blocked polyorganosiloxane having aviscosity ranging from 50 to 10,000 centipoises at 25° C. and a vinylcontent of 0.3 to 30 mole per cent;

3) up to 10 parts by weight of a low molecular weight hydroxy endblocked polyorganosiloxane having a viscosity ranging from 500 to 2,000centipoises at 25° C.;

4) from 5 to 50 parts by weight of a fumed or pyrogenic silica having asurface area ranging from 150 to 450 square m/gm;

5) up to 40 parts by weight of an organohydrogenpolysiloxane crosslinkercontaining at least two silicon-bonded hydrogens per molecule and havinga viscosity ranging from 80 to 1,000 centipoises at 25° C.;

6) from 2 to 500 wppm of a platinum hydrosilylation catalyst;

7) from 0.01 to 3.0 parts by weight of an inhibitor compound; and

8) from 100 to 1,000 wppm of silyl hydrides.

Additional components may include extending fillers, coloring agents,and additives to impart increased performance with respect to certainphysical properties such as oil resistance, heat aging, abrasionresistance and the like.

The functional properties of the resulting rubber elastomer depend notonly on the levels of components but also on the properties of thefiller, additives, and type of curing catalyst. Consequently, theelastomer property profile is highly dependent on the chemical nature ofthe various constituent components as well as the relative proportionsof those components. For example, a heat additive increases thetemperature range of the resulting rubber. Such improvements however, donot necessarily increase the adhesion stability and some times fail toadhere after heat soak.

In seeking to increase the selective adhesion of silicone compositionsto thermoplastic and thermoset substrates, it is frequently desirable toincrease the ability of the silicone to be released from a mating partor surface for which the molded composite may come in contact. These twoproperties collide in that adhesion of the silicone to a thermoplasticor thermoset substrate is desired but ready release from anothersubstrate is necessary for the device to function. For example, thefabrication of connecters requires adhesion of the grommet and facialseal to a thermoplastic closure and also requires that the siliconesurface have sufficient lubricity to allow mating sides to fasten andunfasten with ease.

A typical method of improving the lubricity of a silicone composition issimply to add a liquid component to the formulation that has limitedsolubility in the elastomer and thus the compound bleeds out over time.Ideally such a material itself also has a lubricating quality. Thesecomponents are typically selected from the group of compounds consistingof phenyl containing siloxanes such as copolymers ofpolydimethylsiloxanes, diphenylsiloxane or methylphenylsiloxane, andfluorosiloxanes such as silicones containing trifluoropropyl substitutedsiloxanes.

SUMMARY OF THE PREFERRED EMBODIMENTS

Accomplishment of this selective adhesion is by the addition to adiorganopolysiloxane composition of soluble polydiorganosiloxanes,polycycloorganosiloxanes (linear and cyclic) and/or hydroxy end blockedhydrocarbons (glycols) of a specific molecular distribution preferablyhaving a viscosity of 10 to 1,000 centipoises at 25° C.; and an epoxyfunctional compound, thus giving release characteristics to metalsubstrates while maintaining adhesion to the thermoplastic substrate.

In general, the preferred embodiment of the present invention providesfor a curable silicone elastomer composition comprising:

1) a silicone elastomer;

2) an epoxy functional compound; and

3) a linear and/or cyclic diorganopolysiloxane and/or hydroxy endblocked hydrocarbons (glycols). Examples of such glycols includepolyethylene glycol (e.g., PEG 400) and 1,3 butylene glycol PEG 400 ispreferred.

The foregoing composition may also include a silicone soluble in thecurable elastomer composition. Preferably, the silicone is less solublein the curable elastomer composition when the curable composition hasbeen cured. As a result, the silicone bleeds out of cured composition toimprove lubricity.

The present invention provides a composition that selectively adheres toa substrate that may be a thermoset or a thermoplastic, but not to ametal such as aluminum or steel. The thermoset or thermoplasticsubstrates may be filled polymers with glass or clays. The siliconecompositions of the present invention release readily from metalsubstrates after they have been overmolded, transfer molded or injectionmolded. The present invention further provides for the incorporation ofan adhesion promoter and a self-bleed additive that allows lubricationof the surfaces of the cured silicone simultaneously with adhesion tothe overmolded, transfer molded or injection molded substrate. Theformulations of the present invention demonstrate that compositionscontaining both an adhesion promoter and a self-bleed additive forlubricity can simultaneously achieve the contradictory goals of adhesionto a substrate used in overmolding, transfer or injection molding andrelease from a second substrate where the silicone was not bonded to thesubstrate by the action of the adhesion promoter and the co-moldingprocess of overmolding, transfer molding or injection molding.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

This invention utilizes the release characteristics of solublepolydiorganosiloxanes, polycycloorganosiloxanes (linear and cyclic),and/or hydroxy end blocked hydrocarbons (glycols) of specific moleculardistribution preferably having viscosity of 10 to 1,000 centipoises at25° C. The two (2) additives that provide the selective adhesionproperties are:

1) generally from 0.01 to 30, preferably from 0.01 to 10, morepreferably from 0.05 to 1.0 and even more preferably from 0.10 to 0.50,parts by weight of an epoxy function compound; and

2) generally from 0.01 to 10, preferably from 0.5 to 5 and morepreferably from 1 to 3, parts by weight of soluble polydiorganosiloxanesand/or polycycloorganosiloxanes (linear and/or cyclic) and/or hydroxyend blocked hydrocarbons (glycols), or mixtures thereof.

Generally, it has been found that polybutylene glycols provide betterrelease to metals during molding than poly-dimethyl siloxanes alone.

Optionally, a silicone soluble in the curable elastomer composition canbe added. The silicone is selected such that it is less soluble in thecurable elastomer composition when the curable composition has beencured. As a result, the silicone bleeds out of the cured composition.

In general, one preferred embodiment of the present invention comprisesa curable organopolysiloxane composition having selective adhesion to ametal substrate. The composition should preferably include the followingcomponents:

(A) up to 100 parts by weight of an organopolysiloxane polymer having aviscosity of about 10,000 to about 10,000,000 centipoises at 25° C. withsufficient vinyl, or mixtures of such organopolysiloxane, to providefunctional reactivity to the following crosslinker;

(B) from 0.3 to 40 parts by weight of an organohydrogenpolysiloxanecrosslinker containing at least two silicon-bonded hydrogens permolecule;

(C) a catalytically effective amount of a platinum group metal catalyst;

(D) from 0.01 to 3 parts by weight of a cure inhibitor, preferably ofthe type ethynyl cyclohexanol;

(E) from 0.01 to 30 parts by weight of an adhesion promoter compoundhaving at least one hydroxy group and in the same molecule at least onesubstituent selected from the group consisting of silicon hydride,alkenyl, and acryl;

(F) from 0.01 to 10 parts by weight of an epoxy functional compound; and

(G) up to about 10 parts by weight based on the total composition of acompound selected from the group consisting of solublepolydiorganosiloxanes, polycycloorganosiloxanes (linear and cyclic)and/or hydroxy end blocked hydrocarbons (glycols) and having a specificmolecular distribution such that the viscosity is 50 to 1,000centipoises at 250° C.

Preferably, the organopolysiloxane polymer contains at least twosilicon-bonded lower alkenyl groups in each molecule and is a straightchain organopolysiloxane having a viscosity of about 100,000 to about10,000,000 centipoises at 25° C., or mixtures of suchorganopolysiloxanes, and the lower alkenyl groups are vinyl. Examples oforganopolysiloxanes include Dow Corning Q42901 and Q42903 gums, with anaverage pendant vinyl content ranging from 0.01 to 0.20 mole percentwith 0.80 to 0.20 mole percent being preferable.

Preferably, the organohydrogenpolysiloxane crosslinker has organicsubstituents bonded to silicon atoms, which are more preferably methyl,and the concentration of organohydrogenpolysiloxane provides 0.002 to0.0002 moles of silicon-bonded hydrogen atoms for each mole ofsilicon-bonded alkenyl radicals in the organopolysiloxane polymer, andwherein the crosslinker has the formula:

R¹ ₃Si—(OSiH(R²))_(m)—(OSiR² ₂)_(n)—OSiR¹ ₃

wherein R¹ is independently chosen from a hydrogen or monovalenthydrocarbon radical free of aliphatic unsaturation containing 1 to about8 carbon atoms, R² is independently chosen from a monovalent hydrocarbonradical free of aliphatic unsaturation containing 1 to about 4 carbonatoms, m is one or more, n is one or more, and m+n varies so that thecrosslinker has a viscosity ranging from about 80 to 1000 centipoise at250° C. In addition, R¹ can itself be a polydiorganosiloxane group whichis a straight chain. Where R¹ represents a polydiorganosiloxane, it mayinclude vinyl groups and the crosslinker has a viscosity of 10,000 to10,000,000 centipoise at 25° C. The crosslinker may also comprisemixtures of crosslinkers that fall within the foregoing description.Examples of crosslinkers include Dow Coming 1107 and 63570 cross-linkerswith Dow Corning SYL-OFF® 7678 being preferable.

The platinum group metal catalyst is selected from the group consistingof platinum metal, platinum compounds, platinum complexes and mixturesthereof. Preferably, the platinum group metal catalyst is chloroplatinicacid complexed with a liquid olefin or an organosiloxane containingethylenically unsaturated hydrocarbon radicals bonded to silicon. Morepreferably, the platinum group metal catalyst is a neutralized complexof chloroplatinic acid or platinum dichloride withdivinyltetramethyldisiloxane.

In general, the platinum group metal catalyst provides about 0.1 toabout 500 parts by weight platinum group metal per million parts of thecombined weights of organopolysiloxane and organohydrogenpolysiloxane.Preferably, the platinum group metal catalyst provides about 1 to about50 parts by weight platinum group metal per million parts of thecombined weights of organopolysiloxane and organohydrogenpolysiloxane.

In general, the cure inhibitor compound is an acetylene alcoholderivative such as ethynyl cyclohexanol or pyridine alcohol having thefollowing general formula:

R′R(OH)_(x)

Where R′ is an alkyne unsaturated hydrocarbon chain, branched orunbranched, and R is a saturated hydrocarbon linear or cyclic withhydroxy groups pendant or end blocked with hydroxy saturation indicatedby x, which is 1 to complete hydroxy saturation of the R group.

In general, the adhesion promoter is a hydroxinated silicone compound ofthe formula:

(OH)(R¹)₂SiO(—SiO(R²)₂—)zSi(R¹)₂(OH)

Where R¹ is any hydrocarbon alkyl or alkenyl radical linear or branchedcomprising not more than 10 carbon atoms, R² is any mixture of anyalkyl, alkenyl, aliphatic, or aromatic radical, linear or branched, upto 12 carbon atoms, and where z is of sufficient number to create aviscosity of about 50 to about 10,000 centipoises at 25° C. In generalfrom 0.01 to 30, preferably from 0.05 to 2, and more preferably from 0.5to 1, parts per weight are used. Examples include 1-hydroxy 2,3 methylendblocked vinylmethyl siloxane (DP 10 to 12 with 2 to 4 pendant vinylgroups).

In general, the epoxy-functional compound isglycidoxypropyltrialkoxysilane having the formula:

wherein R denotes a methyl or ethyl radical. The embodiment wherein R isa methyl group is particularly preferred.Glycidoxypropyltrimethoxysilane may also include quantities ofmethacrylvinylpolysilane, chlorotrimethoxysilane, vinyltrimethoxysilane,and divlnyldimethoxysilane. In general, from 0.01 to 30, preferably,from 0.05 to 10, and more preferably, from 0.1 to 0.05 parts by weightare used.

The polydiorganosiloxanes include Dow Corning 200 fluid. Viscositygrades 50 to 200 are preferable and grades 50 to 10,000 in general. Anexample of polycycloorganosiloxanes includes Dow Corning 244 fluid andother cyclic siloxanes from D4 to D10 (DP units), preferably D 4 and D5.The molecular distribution should be such as to produce a viscosity at25° C. of 50 to 1,000, preferably 50 to 500 centipoises, and morepreferably 50 to 200 centipoises.

In another embodiment of the present invention, the epoxy-functionalcompound is glycidoxypropyltrimethoxysilane. Preferably, theepoxy-functional compound comprises about 0.01 to 10 parts by weight per100 weight parts of organopolysiloxane polymer.

The composition according to the present invention can include a fillerselected from the group consisting of fumed silica, treated fumedsilica, precipitated silica, treated precipitated silica, fused silica,and finely divided quartz and mixtures thereof.

In yet another embodiment of the present invention, a composite isformed having bonded thereto a cured organopolysiloxane composition. Thecomposition preferably contains the following components:

(A) up to 100 parts by weight of an organopolysiloxane polymer having aviscosity of about 10,000 to about 10,000,000 centipoises at 25° C. withsufficient vinyl, or mixtures of such organopolysiloxane to providefunctional reactivity of a crosslinker organohydrogenpolysiloxane;

(B) from 0.3 to 40 parts by weight of an organohydrogenpolysiloxanecrosslinker containing at least two silicon-bonded hydrogens permolecule;

(C) a catalytically effective amount of a platinum group metal catalyst;

(D) from 0.01 to 3 parts by weight of a cure inhibitor, preferably ofthe type 4 or 5, ethyl cyclohexan-1-ol;

(E) from 0.01 to 30 parts by weight of a compound comprising at leastone hydroxy group and in the same molecule at least one substituentselected from the group consisting of silicon hydride, alkenyl, andacryl;

(F) from 0.01 to 10 parts of an epoxy functional compound; and

(G) up to about 10 parts by weight based on the total composition of acompound selected from the group consisting of a solublepolydiorganosiloxanes, polycycloorganosiloxanes (linear and cyclic)and/or hydroxy end blocked hydrocarbons (glycols) and having a specificmolecular distribution such that the viscosity is 50 to 1,000centipoises at 25° C.

In still yet another embodiment of the present invention, a compositecontaining an epoxy-coated substrate having bonded thereto a curedorganopolysiloxane composition is formed. The composition preferablycomprises:

(A) up to 100 parts by weight of an organopolysiloxane polymer having aviscosity of about 10,000 to about 10,000,000 centipoises at 25° C. withsufficient vinyl, or mixtures of such organopolysiloxane to providefunctional reactivity of the following crosslinker;

(B) from 0.3 to 40 parts by weight of an organohydrogenpolysiloxanecrosslinker containing at least two silicon-bonded hydrogens permolecule;

(C) a catalytically effective amount of a platinum group metal catalyst;

(D) from 0.01 to 3 parts by weight of a cure inhibitor, preferably ofthe type 4 or 5, ethyl cyclohexan-1-ol;

(E) from 0.01 to 30 parts by weight of a compound comprising at leastone hydroxy group and in the same molecule at least one substituentselected from a group consisting of silicon hydride, alkenyl and acryl;

(F) from 0.01 to 10 parts of an epoxy functional compound; and

(G) up to about 10 parts by weight based on the total composition of acompound selected from the group consisting of solublepolydiorganosiloxanes, polycycloorganosiloxanes (linear and cyclic)and/or hydroxy end blocked hydrocarbons (glycols) and having a specificmolecular distribution such that the viscosity is 50 to 1,000centipoises at 250° C.

In a preferred embodiment, the substrate is metal. The epoxy coatingcomprises chemistries used in cast, form in place, or vacuum bag cures.Moldable epoxy composites are preferable.

Preferably, a silicone soluble in the curable elastomer composition isadded. In general, the silicone is less soluble in the curable elastomercomposition when the curable composition has been cured. In such case,the silicone bleeds out of the cured composition. Preferably, thesilicone is selected from the following or mixtures thereof:

(A) phenyl containing siloxanes such as copolymers of diphenylsiloxanewith diorganosiloxanes and copolymers of methylphenylsiloxane withdiorganosiloxanes, more preferably dimethylsiloxanes, having a viscosityranging between about 10 to about 10,000 centipoises at 25° C.,preferably ranging from about 100 to about 1000 centipoises at 250° C.;and

(B) fluorosiloxanes such as silicones containing trifluoropropylsubstituted siloxanes, having a viscosity ranging between 100 to about10,000 centipoises at 25° C., preferably ranging from about 100 to about1000 centipoises at 25° C.

Examples of the foregoing include phenyl siloxanes commonly sold as DowCorning 550 Fluid or GE SF-1154 and those for fluorosiloxanes FS-149,FS150-10M FS157 all of various viscosities and purity grades. Thesecomponents lubricate without adversely affecting the adhesion of thecomposition to a substrate.

The resins to which the cured inventive composition can be bondedinclude Nylon, polyphenylene, polyphthalamide, polyphenylene ether,polyamide and polyimid thermoplastic resins that may or may not be glassfilled, mineral filled, or carbon filled. Further, thermoset resins suchas epoxy, silicone or others that are manufactured by coating asubstrate or by direct casting can be bonded to the curedorganopolysiloxane composition in of the present invention. Preferablythe resin is PBA or PBT.

Additional components may include extending fillers, coloring agents,and additives to impart increased performance with respect to certainphysical properties such as oil resistance, heat aging, abrasionresistance and the like.

All such compositions have selective adhesion to polymer substrates anddo not have significant adhesion to metal surfaces. The significance ofselective adhesion preferably is such that the adhesion to metal ingeneral is such that the composition sticks to a resin or epoxy coatedsubstrate, but not to metal. Preferably, the adhesion to metal is lessthan half the adhesion to the target polymer substrate and morepreferably has no cohesion failure to the metal as determined by lapshear testing.

EXAMPLES

Curable silicone rubber compositions were prepared from a highconsistency silicone rubber base. Adhesion components E through G wereadded in amounts shown in Table 1. Samples of these materials were madeby curing the composition at 150° C. for 3 minutes. These samples weretested per ASTM D816. The results are listed in Table 1.

TABLE 1 Adhesion Components (parts by weight) % cohesion failure tolisted substrate Run E F G H Steel PPA Nylon  0 0 0 0 0 0 0 0  1 3.000.10 0.5 1.00 0 50 60  2 3.00 0.20 0.5 1.00 0 70 80  3 3.00 0.35 0 0.5020 80 90  4 5.00 0.35 0 1.00 0 90 95  5 7.00 0.35 0 1.50 0 95 100  63.00 0.50 0 1.00 5 100 100  7 5.00 0.50 0 1.50 10 100 100  8 7.00 0.50 01.50 20 100 100  9* 5.00 0.35 0 1.00 0 95 90 10 5.00 0.35 0 0.2 10 100100 11 5.00 0.35 0.5 0.3 0 100 100 12 5.00 0.35 0.5 0.4 0 100 100 135.00 0.35 0.5 0.5 0 90 95 Component E - adhesion promoter: Hydroxyl EndBlocked, polysiloxane Component F - Epoxy functional compound:Glycidoxypropyltrimethoxysilane Component G - Selective releaseadditive: Trimethyl end blocked polysiloxane Component H - PolyethyleneGlycol (PEG 400) 9* - Had 1.0 parts by weight Polymethylphenylsiloxaneas a self-lubricant

In the first example in Table 1 no adhesion promoting compounds wereadded to the compound as a control (Run 0). Example Runs 1-13 showadditions of adhesion promoting compounds. Example Run 9 shows thataddition of polymethylphenylsiloxane as a lubricant does notdeleteriously affect adhesion.

The examples demonstrate that improved adhesion is achieved by additionof components E and F. Specifically to this invention is that additionof component G and H in combination with component E and F maintainsadhesion to plastic but does not adhere significantly to steel. Aself-lubricating version of the optimal run 4 was replicated to showthat select adhesion was unaffected. By this fact, the composition issaid to be a selective adhesion promoting material with good adhesion tothermoplastics and thermosets yet not to metal surfaces and can be selflubricating.

TABLE 2 Liquid Silicone Rubber Evaluations % Cohesion failure 1 tolisted Adhesion Components substrate Run E F G H Steel PPA Nylon 14 0.50.35 0.8 0 0 10 20 15 0.5 0.35 1.4 0 15 25 35 16 0.5 0.4 0.8 0 0 20 3017 0.5 0.4 1.4 0 10 40 50 18 0.5 0.61 0.8 0.35 0 60 100 19 0.5 0.76 0.80.5 0 65 100 Component E - Glycidoxypropyltrimethoxysilane Component F -Hydroxyl End Blocked Polydimetylmethylvinylsiloxane Component G -Polydimethylsiloxane 100CS Component H - Polyethylene Glycol (PEG 400)

Table 2 demonstrates that, as in High Consistency Rubber (“HCR”) HCR,Liquid Silicone Rubber (“LSR”) has improved adhesion by addition ofcomponents E and F. Specifically to this invention is that addition ofcomponent G and H in combination with component E and F maintainsadhesion to plastic but does not adhere significantly to steel. By thisfact, the composition is said to be a selective adhesion promotingmaterial with good adhesion to thermoplastics and thermosets yet not tometal surfaces and can be self lubricating.

Physical properties of said runs meet common commercial and militaryspecifications. These specifications are exemplified in specificationA-A-59588 (Formally ZZ-R-765). Generally, through compounding options,they can be made to meet all classes and grades. Other considerationssuch as fluorosilicone specifications such as Mil-R-25988 can also beregarded as passable by these compositions in terms of class and gradecallouts. Table 3 notes some of physical property testing and thepropensity of such formulation to meet rigorous requirements.

TABLE 3 Physical Properties Originals Tear Compression Set 22 Heat Age70 hrs @ Die hrs @ 1770 C. 1770 C. Material Durometer Tensile ElongationB NPC W/PC Durometer Tensile Elongation Type Shore A psi % ppi % % ShoreA psi % HCR 53 1298 606 177 23 18 59 1164 546 LSR 51 1240 704 263 14 856 269 941 ppi = Pounds Per Inch NPC = No Post Cure W/PC = Without PostCure

In table 3 representative examples of HCR and LSR were chosen asexamples of physical property performance. The data presented in thistable is from the optimal runs 5 and 18 for HCR and LSR, respectively.These data sets are typical physical property performance. Modificationsto the formulations may yield additional performance safety to theprescribed specification callouts.

The embodiments of the present invention recited herein are intended tobe merely exemplary and those skilled in the art will be able to makenumerous modifications to them without departing from the spirit of thepresent invention. All such modifications are intended to be within thescope of the present invention as defined by the claims appended hereto.

What is claimed is:
 1. A curable organopolysiloxane composition havingselective adhesion to a substrate, said composition containing thefollowing components: (A) an organopolysiloxane polymer; wherein thereis up to 100 parts by weight of the organopolysiloxane polymer having aviscosity of about 10,000 to about 10,000,000 centipoises at 25° C. withsufficient vinyl, or mixtures of such organopolysiloxane to providefunctional reactivity with a crosslinker organohydrogenpolysiloxane; (B)an organohydrogenpolysiloxane crosslinker; wherein there is from 0.3 to40 parts by weight of the organohydrogenpolysiloxane crosslinkercontaining at least two silicon-bonded hydrogens per molecule; (C) aplatinum group metal catalyst; wherein there is a catalyticallyeffective amount of the platinum group metal catalyst; (D) a cureinhibitor; wherein there is from 0.01 to 3 parts by weight of the cureinhibitor of the type ethynyl cyclohexanol; (E) an adhesion promoter;wherein there is from 0.01 to 30 parts by weight of a compoundcomprising at least one hydroxy group and in the same molecule at leastone substituent selected from a group consisting of silicon hydride,alkenyl, and acryl; (F) an epoxy functional compound; wherein there isfrom 0.01 to 30 parts by weight of the epoxy functional compound; and(G) a compound selected from the group consisting of solublepolydiorganosiloxanes, polycycloorganosiloxanes, glycols, and mixturesthereof; wherein there is up to about 10 parts by weight based upon thetotal composition of a mold release agent compound that is selected fromthe group consisting of soluble fluid polydiorganosiloxanes,polycycloorganosiloxanes (linear and cyclic), hydroxy end blockedhydrocarbons and having a molecular distribution such that the viscosityis 50 to 10,000 centipoises at 25° C.
 2. The composition of claim 1wherein there is from 0.1 to 10 parts by weight of the crosslinker.
 3. Acomposite comprising an epoxy-coated substrate having bonded thereto acured organopolysiloxane, said cured organopolysiloxane compositionhaving selective adhesion to the epoxy-coated substrate, saidcomposition containing the following components: (A) anorganopolysiloxane polymer; (B) an organohydrogenpolysiloxanecrosslinker; (C) a platinum group metal catalyst; (D) a cure inhibitor;(E) an adhesion promoter; (F) an epoxy functional compound; and (G) acompound selected from the group consisting of solublepolydiorganosiloxanes, polycycloorganosiloxanes, glycols, and mixturesthereof.
 4. The composite of claim 3, where the substrate is metal.